Electrical protective system



April 16,1935.

L. W. THOMPSON ELECTRICAL PROTECTIVE SYSTEM Original Filed July 21';1932 His AtCOF'hC-tg.

Patented Apr. 16, 1935 v y I UNITED STATES PATENT OFFICE 1,999,295ELECTRICAL rno'rrcrivs SYSTEM Louis W. Thompson, Schenectady, N; Y.,asaignor to General Electric Company, .a corporation of New YorkApplication July 21, 1932, Serial No. 623,756

Renewed August 16, 1934 6 Claims. (Cl. 171-312) .My invention relatesbroadly to electrical prothe assignee oi. the present application.Regutective systems, and more particularly to an aulater 8 comprises avoltage responsive control tomatic system for limiting the temperaturerisemember in the form of a torque motor I which of dynamo-electricmachines. is connected to respond to the voltage of circuit The presentinvention is a modification of th 3 through suitable potentialtransformer la. Mo- 5 invention which is disclosed and claimed in anaptor I is connected to produce a clockwise torque plication of E. M.Hunter, Serial No. 623,749, filed which is arranged to be exactlybalanced, at .a a July 21, 1932, and assigned to the assignee of thenormal voltage on circuit 3, by a spring 8. An present application. Inthe Hunter application oil-pot 9 serves to dampen the motion 01 motor 10the temperature rise of the dynamo-electric ma- 1 and improve the actionof the regulator. Ar- 10 chine is limited to a maximumvalue by meansranged to be moved by motor 1 are low speed of a voltage relay which isconnected to be reraise and lower contacts it! and II, respectively,sponsive to the voltage of the field winding of and high speed raise andlower contacts l2 and the dynamo-electric machine and which controls l3,respectively. Contacts l0 and l I are arranged the means for varying theexcitation of this field to contact with a center contact member it,while is winding. The theory is that the temperature rise contacts I!and I! are arranged to contact with of a dynamo-electric machine isordinarily suba center contact member is. Under the control stantiallyproportional to the watts dissipated in of low speed raise and lowercontacts to and H its field winding and the steady state voltage isareversible pilot motor l6 which is arranged to across the field windingordinarily bears a suboperate a rheostat I! connected in the field wind-20 stantially direct relation to the watts dissipated. ing circuit ofexciter 5. Under the control of In accordance with my invention I modiiythe high speed raise and lower contacts l2 and I3 action of the voltageresponsive device in such a are a pair of relays, or -contactors, l8 andI9, remanner that the voltage at which the device is spectively,Contactor I! has its contacts noractuated varies substantially inverselywith the mally open and is arranged to short circuit the 25 load on themachine. The reason for doing this entire rheostat I! when it isactuated. Conis that the degree of excitation of a dynamo tactor I!normally has its contacts closed and is electric machineis not alwayssubstantially proarranged to normally short circuit a resistanceportional to its total losses, and consequently, 20 which is connectedin the field circuit of exto its overall temperature rise. For example,'a citer 5. When contactor I9 is actuated, it opens 30 synchronouscondenser may sometimes have to its contacts and-thereby inserts theresistance 20 be operated under-excited so as to supply large in thefield circuit of the exciter thereby lowering lagging currents which maycause severe overthe voltage 0! the exciter consequently the enloadingand heating, although the watts dissiergization of the field winding 4of the machine I.

'35 pated in the field winding are relatively small. Arranged to controlthe action of the regulator An object of my invention is to provide anew n r asin the excitation of the W i 4 1 and improved electricalprotective system. a relay 2| having a pair 01' normally closed con- Myinvention will be better understood rrom tacts 22. These contacts areconnected in the the following description taken in connection circuitfor the motor I6 which is controlled by the 40 with the accompanyingdrawing, and its scope low speed raise contact [9. Relay 2| is also pro-4 .will be pointed out in the appended claims, vided with a pair ofnormally open contacts 23 Referring now to the single figure oi theacwhich are in an energ c i for a t companying drawing,,in which I haveillustrated lay relay 2!. Relay 24 has a pa r of normallydiagrammatically one embodiment of my invenclosed contacts 25 which areconnected in the tion, I is a dynamo-electric machine which, itenergizin ir uit f r the 1118 Speed raise relay 45 will be assumed, is'asynchronous condenser, and It. This circuit is controlled by the highspeed which has an armature 2 connected to a circuit raise contact I2.Relay 2| is arranged to be ac- 3, and field winding 4 connected to beenergized tuated by a voltage winding 28 connected to reby an exciter 5.I may control the voltage oi spond to the voltage of field winding 4.Ar-

exciter I and consequently the'excitation 0! maranged tooppose voltagecoil 26 isabiaslng spring 50 chine I in any manner and, as illustrativeof 21. .A coil, or winding, 20 which is energized in one suchcontrolling arrangement, I have shown accordance with the load, oroutput, of machine an automatic voltage regulator 9 oi the type I actscumulatively-with respecttovoltage windwhich is disclosed and claimed inmyPatent No. ing 28. As this machine is provided with 9. volt-1,848,952, granted March 8, 1932, andasslgnedto age regulator, itsvoltage is substantially conto stant. Therefore, its current will beproportional to its volt-ampere output, or load, and consequently coil28 is connected in circuit 3, through a suitable current transformer 29,so as to respond to the current in the machine i.

A suitable source of current, such as a direct current supply bus 30,isprovided for operating the motor I 6 and the relays l8, l9 and 24.Center contacts l4 and I5 are connected to the positive side of thesupply circuit 30 through a conductor 3i.

Regulator 6 operates as follows: If the voltage of circuit 3 is slightlybelow normal the torque of motor 1 will be overcome by the countertorque of spring 8 and low speed raise contact M will come intoengagement with center contact l4. When this happens a circuit iscompleted for motor l6 as follows: Conductor 3|, contacts l4 and I0,contacts22 of relay 2|, the motor it through its upper field winding,and back to the negative side of the supply circuit through a conductor32. This energization of motor 16 is such as to cause it to operate inthe proper direction to decrease the resistance value of rheostat I1 andthereby increase the excitation of the exciter 5 and consequentlyincrease the excitation and voltage of the main machine. This operationof rheostat i1 is such as to increase the energization of field winding4 in relatively small increments. If the voltage of circuit 3 isconsiderably below normal contact ID will be flexed and contact I2 willengage contact l5, thereby completing an energizing circuit for highspeed raise contactor I8 as follows: Conductor 3i, contacts 15 and I2,contacts 25 of relay, the operating coil of relay l8 and conductor 32.The operation of relay l8 removes the entire rheostat I! from the fieldcircuit of exciter 5 and thereby increases the excitation of winding 4in a relatively large increment. 0n relatively slight and largeincreases in voltage above normal the torque of motor 1 overcomes thecounter torque of spring 8 and contacts II and I3 will successivelyengage their respective center contacts l4 and 15. This will complete anenergizing circuit for motor I6 and an energizing circuit for contactorl9, through conductors 33 and 34 respectively, thereby to reduce theenergization of field winding 4 in relatively small and relatively largeincrements, respectively.

If the operating conditions on circuit 3 necessitate a largeenergization of field winding 4 its voltage may reach such a. high valueas to correspond to a. watt input which corresponds to a limiting valueof temperature rise for the machine. When this takes place the voltagerelay 2! is actuated thereby opening its contacts 22 and closing itscontacts 23. The opening of contacts 22 prevents the voltage regulatorfrom producing relatively slow increases in excitation. The closing ofcontacts 23 causes the actuation of time delay relay 24 which, in apredetermined time, opens its contacts 25 and thereby breaks the circuitfor the quick raise relay l8, thereby preventing the voltage regulatorfrom producing relatively rapid increases in excitation. The effect ofthe current winding 28 is to lower the voltage 'at which relay 2| isactuated substantially inversely with the value of the load, or current,of machine I. As the current in the armature of machine I also producesa heating effect and as the heating eifect thus produced is notnecessarily directly related to the heating effect of the field winding,it will be desirable (to limit the maximum excitation or voltage of themain field winding, inversely with the load on the main machine. Thus,as the load increases the pull of magnet 28 increases so that thecombined pull of coils 28 and 28 will overcome the pull of biasingspring 21 at lower values of field voltage when the armature current ofmachine I is at higher values.

While I have shown and described a particular embodiment of myinvention, it will be obvious to those skilled in the art that changesand modifications may be made without departing from my invention, and Itherefore aim in the appended claims to cover all such changes andmodifications as fall within the true spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

1. In combination, a dynamo-electric machine having a field winding, andmeans for limiting the voltage of said field winding to a maximum valuewhich varies inversely with the load on said machine.

2. In combination, a dynamo-electric machine having a field winding,means for varying the excitation of said field winding, means responsiveto the voltage across said field winding for causing said excitationvarying means to limit the voltage across said field winding to amaximum value, and means responsive to the current in saiddynamo-electric machine for varying said maximum value inversely withthe value of said current.

3. In combination, a dynamo-electric machine having a field winding, anautomatic regulator of an operating condition of said machine for varyinthe excitation of said field winding, meansresponsive to the voltageacross said field winding for causing said regulator to limit saidexcitation to a value corresponding to a maximum field voltage, andmeans responsive to the current in said machine for causing said voltageresponsive means to vary said maximum voltage inversely with the currentin said machine.

4. In combination, a dynamo-electric machine field winding in relativelysmall and large in-' crements depending respectively upon whether thevoltage of said machine is a relatively small or large amount below anormal value, relay means responsive to the voltage of said fieldwinding for preventing said regulator from increasing the energizationof said field winding when its voltage exceeds a maximum value, timedelay means for preventing limitation of the action of said regulator inproducing said relatively large increases in energlzation for apredetermined time after said maximum field voltage is attained, andmeans responsive to increases in current in said machine for causingsaid relay means to operate at lower values of maximum field voltage.

6. In combination, a dynamo-electric machine having a field winding, anautomatic regulator mosses l 3 oi an operating condition of said machinefor electric machme whereby said regulator will he varying theenergization of said neld winding, prevented irom increasing theenergizatlon of land a relay for preventing said regulator irom saidfield winding when the voltage acros said increasing the energization ofsaid field windileld winding reaches a maximum value which s-ing. saidrelay having a pair 0! cumulatively varies inversely with the current insaid dy- 5 acting operating windings connected respectivenamo-eleciu'icmachine.

iv to be responsive to the voltage across said iield winding and to thecurrent in said dynamo- LOUIS W. THOMPSON.

